Paralleling UPS Batteries

B

Bennett Price

Guest
Several weeks ago I posted a query here about the advisability and/or
precautions to take in paralleling batteries for a UPS, (an APC Smart
UPS-700 Net). It normally takes one pair of 12v 7AH batteries, from
which I was getting ~5-7 minutes of run time with a 65% load (as
reported by APC Powerchute Biz Edition 7.119).

Jerry G, Roni L. and Kris S. warned that the recharge might not be
sufficient and to check float voltages with and w/o batteries
paralleled, to use batteries of comparable vintage, and to be sure extra
long run time didn't cause overheating.

I built an appropriate 12 Gauge cable and used the Run Time calibration
feature of the APC software. 4 batteries gave me no more run time than
pair A or pair B alone. I carefully rechecked connections, made sure no
connector was running hot and end up w. the same results. 4 batteries
give me the same run time as either pair. Total float current is about
12.5ma, 5ma on pair B, 7.5 on pair A).

I'm stumped. I've set things up so that I just pull off or stick back
on just one spade lug every time I do the test. What is going on?
I should be getting at least 2x the run time, (more since the slower
the consumption the more AH the battery yields.)

Any suggestions more than welcome.
 
What is the "APC run time calibration feature?" Perhaps if you explained
the criteria for "run time" that you are using. How do you determine that
all the batteries are fully charged under both test scenarios? How do you
measure when they are exhausted? These answers may help us to understand
your test methodology and explain your (unexpected) results.

Also, as an aside, what is the maximum current being drawn from the
batteries under load? The 12 gauge wire seems a bit on the high (resistive)
end to me, but this would be dependent on the current and the distance

Bob

"Bennett Price" <bjpriceNOSPAM@itsa.ucsf.edu> wrote in message
news:Uk_8c.43044$PR7.24947@newssvr25.news.prodigy.com...
Several weeks ago I posted a query here about the advisability and/or
precautions to take in paralleling batteries for a UPS, (an APC Smart
UPS-700 Net). It normally takes one pair of 12v 7AH batteries, from
which I was getting ~5-7 minutes of run time with a 65% load (as
reported by APC Powerchute Biz Edition 7.119).

Jerry G, Roni L. and Kris S. warned that the recharge might not be
sufficient and to check float voltages with and w/o batteries
paralleled, to use batteries of comparable vintage, and to be sure extra
long run time didn't cause overheating.

I built an appropriate 12 Gauge cable and used the Run Time calibration
feature of the APC software. 4 batteries gave me no more run time than
pair A or pair B alone. I carefully rechecked connections, made sure no
connector was running hot and end up w. the same results. 4 batteries
give me the same run time as either pair. Total float current is about
12.5ma, 5ma on pair B, 7.5 on pair A).

I'm stumped. I've set things up so that I just pull off or stick back
on just one spade lug every time I do the test. What is going on?
I should be getting at least 2x the run time, (more since the slower
the consumption the more AH the battery yields.)

Any suggestions more than welcome.
Click to expand...
 
Bob Shuman wrote:

What is the "APC run time calibration feature?" Perhaps if you explained
the criteria for "run time" that you are using. How do you determine that
all the batteries are fully charged under both test scenarios? How do you
measure when they are exhausted? These answers may help us to understand
your test methodology and explain your (unexpected) results.

Also, as an aside, what is the maximum current being drawn from the
batteries under load? The 12 gauge wire seems a bit on the high (resistive)
end to me, but this would be dependent on the current and the distance

Bob

"Bennett Price" <bjpriceNOSPAM@itsa.ucsf.edu> wrote in message
news:Uk_8c.43044$PR7.24947@newssvr25.news.prodigy.com...

Several weeks ago I posted a query here about the advisability and/or
precautions to take in paralleling batteries for a UPS, (an APC Smart
UPS-700 Net). It normally takes one pair of 12v 7AH batteries, from
which I was getting ~5-7 minutes of run time with a 65% load (as
reported by APC Powerchute Biz Edition 7.119).

Jerry G, Roni L. and Kris S. warned that the recharge might not be
sufficient and to check float voltages with and w/o batteries
paralleled, to use batteries of comparable vintage, and to be sure extra
long run time didn't cause overheating.

I built an appropriate 12 Gauge cable and used the Run Time calibration
feature of the APC software. 4 batteries gave me no more run time than
pair A or pair B alone. I carefully rechecked connections, made sure no
connector was running hot and end up w. the same results. 4 batteries
give me the same run time as either pair. Total float current is about
12.5ma, 5ma on pair B, 7.5 on pair A).

I'm stumped. I've set things up so that I just pull off or stick back
on just one spade lug every time I do the test. What is going on?
I should be getting at least 2x the run time, (more since the slower
the consumption the more AH the battery yields.)

Any suggestions more than welcome.



Thanks for responding
Click to expand...

APC software calculates runtime by drawing down the batteries to 25%
capacity. They float at 27.87 and cut off (w. 25% left) at 22.74
(according to APC's hw+sw). APC sw then calculates the run time based
on these figures.

Fully charged to me means that Pair A, Pair B, and Pairs A+B all float
at the same voltage with minimal (<15 ma) current (and lots of recharge
time between tests). Cables total perhaps 18" in length and don't run
appreciably warm). I haven't measured discharge current but the load
is about 350-400VA which implies a current (@ 25 volts) of about 14A
plus some more for heat - maybe 20A at most - well within capability of
12Ga wire. (APC sw calculates the load at around 65% (of a 700VA UPS).
 
Thanks. I agree that the 12 gauge wire is fine up to about 20A. I wasn't
sure of the load so assumed it was much larger, drawing higher current.

On the "discharged" condition (22.74V), this sounds to me like you could
have a weak battery (or even two of the batteries in the series set)
"pulling down" the voltage across the other (better) set of batteries. If
you think about this, in addition to supplying current to the actual load,
since they are in parallel, the good batteries are also forced to supply
"charging current" to the other series batteries since their voltage is
likely lower (they likely are running down more quickly since they are not
holding as much charge or possibly did not start with as much charge). In
essence, the benefit of the extra current that is supplied (from the bad
batteries) when those batteries are fully charged could be getting consumed
as additional current drawn from the "good set" by the "bad set" as their
voltage drops more quickly. This is all theory, but you might be able to
verify that this is happening by using diodes to isolate each of the series
battery sets while they are "discharging" to prevent this from happening.
If you see dramatic improvement in runtime, this would support this theory.

Good luck and let us know what you find out.

Bob

"Bennett Price" <bjpriceNOSPAM@itsa.ucsf.edu> wrote in message
news:40647C63.6090002@itsa.ucsf.edu...
Thanks for responding

APC software calculates runtime by drawing down the batteries to 25%
capacity. They float at 27.87 and cut off (w. 25% left) at 22.74
(according to APC's hw+sw). APC sw then calculates the run time based
on these figures.

Fully charged to me means that Pair A, Pair B, and Pairs A+B all float
at the same voltage with minimal (<15 ma) current (and lots of recharge
time between tests). Cables total perhaps 18" in length and don't run
appreciably warm). I haven't measured discharge current but the load
is about 350-400VA which implies a current (@ 25 volts) of about 14A
plus some more for heat - maybe 20A at most - well within capability of
12Ga wire. (APC sw calculates the load at around 65% (of a 700VA UPS).
Click to expand...
 
Bob Shuman wrote:

Thanks. I agree that the 12 gauge wire is fine up to about 20A. I wasn't
sure of the load so assumed it was much larger, drawing higher current.

On the "discharged" condition (22.74V), this sounds to me like you could
have a weak battery (or even two of the batteries in the series set)
"pulling down" the voltage across the other (better) set of batteries. If
you think about this, in addition to supplying current to the actual load,
since they are in parallel, the good batteries are also forced to supply
"charging current" to the other series batteries since their voltage is
likely lower (they likely are running down more quickly since they are not
holding as much charge or possibly did not start with as much charge). In
essence, the benefit of the extra current that is supplied (from the bad
batteries) when those batteries are fully charged could be getting consumed
as additional current drawn from the "good set" by the "bad set" as their
voltage drops more quickly. This is all theory, but you might be able to
verify that this is happening by using diodes to isolate each of the series
battery sets while they are "discharging" to prevent this from happening.
If you see dramatic improvement in runtime, this would support this theory.

Good luck and let us know what you find out.

Bob

"Bennett Price" <bjpriceNOSPAM@itsa.ucsf.edu> wrote in message
news:40647C63.6090002@itsa.ucsf.edu...

Thanks for responding

APC software calculates runtime by drawing down the batteries to 25%
capacity. They float at 27.87 and cut off (w. 25% left) at 22.74
(according to APC's hw+sw). APC sw then calculates the run time based
on these figures.

Fully charged to me means that Pair A, Pair B, and Pairs A+B all float
at the same voltage with minimal (<15 ma) current (and lots of recharge
time between tests). Cables total perhaps 18" in length and don't run
appreciably warm). I haven't measured discharge current but the load
is about 350-400VA which implies a current (@ 25 volts) of about 14A
plus some more for heat - maybe 20A at most - well within capability of
12Ga wire. (APC sw calculates the load at around 65% (of a 700VA UPS).



Interesting thought. What I'll do is swap some batteries around and see
Click to expand...
what happens. Now I'm using (A1+A2) + (B1+B2). I'll change that to
(A1+B2) with/without (A2+B1). If I've got two bad batteries, after
swapping them I should have one good set and one poor set.
 
"Bob Shuman" <reshuman@removethis.lucent.com> wrote in message
news:c421gs$hep@netnews.proxy.lucent.com...
Thanks. I agree that the 12 gauge wire is fine up to about 20A. I wasn't
sure of the load so assumed it was much larger, drawing higher current.

On the "discharged" condition (22.74V), this sounds to me like you could
have a weak battery (or even two of the batteries in the series set)
"pulling down" the voltage across the other (better) set of batteries. If
you think about this, in addition to supplying current to the actual load,
since they are in parallel, the good batteries are also forced to supply
"charging current" to the other series batteries since their voltage is
likely lower (they likely are running down more quickly since they are not
holding as much charge or possibly did not start with as much charge). In
essence, the benefit of the extra current that is supplied (from the bad
batteries) when those batteries are fully charged could be getting
consumed
as additional current drawn from the "good set" by the "bad set" as their
voltage drops more quickly. This is all theory, but you might be able to
verify that this is happening by using diodes to isolate each of the
series
battery sets while they are "discharging" to prevent this from happening.
If you see dramatic improvement in runtime, this would support this
theory.

Good luck and let us know what you find out.

Bob

"Bennett Price" <bjpriceNOSPAM@itsa.ucsf.edu> wrote in message
news:40647C63.6090002@itsa.ucsf.edu...
Thanks for responding

APC software calculates runtime by drawing down the batteries to 25%
capacity. They float at 27.87 and cut off (w. 25% left) at 22.74
(according to APC's hw+sw). APC sw then calculates the run time based
on these figures.

Fully charged to me means that Pair A, Pair B, and Pairs A+B all float
at the same voltage with minimal (<15 ma) current (and lots of recharge
time between tests). Cables total perhaps 18" in length and don't run
appreciably warm). I haven't measured discharge current but the load
is about 350-400VA which implies a current (@ 25 volts) of about 14A
plus some more for heat - maybe 20A at most - well within capability of
12Ga wire. (APC sw calculates the load at around 65% (of a 700VA UPS).


I think you hit it there. Batteries in parralel need diodes to prevent that
Click to expand...
very thing. Also is why I did simular on my ups, had 1 small 12 battery,
so I removed it and connected a larger 12 in its place - external to the
case. Been running over a year that way with no probs. and about 3 times
the running time.
 
In article <07s9c.7131$ol3.2135@fe03.usenetserver.com>,
jtech <toomuch@spam.net> wrote:

I think you hit it there. Batteries in parralel need diodes to prevent that
very thing.
Click to expand...
Unfortunately, the voltage drop across the diode when loaded will make the
UPS see the battery as "empty" before it really is. Just like an older
Lead-Acid will get a little bit high resistance, and will sag on-load,
leading to the UPS switching off early, thinking that the battery is about
to expire.

Hard to beat this one without just using newer, bigger batteries :)
--
--------------------------------------+------------------------------------
Mike Brown: mjb[at]pootle.demon.co.uk | http://www.pootle.demon.co.uk/
 
Several weeks ago I posted a query here about the advisability and/or
precautions to take in paralleling batteries for a UPS, (an APC Smart
UPS-700 Net). It normally takes one pair of 12v 7AH batteries, from
which I was getting ~5-7 minutes of run time with a 65% load (as
reported by APC Powerchute Biz Edition 7.119).

Jerry G, Roni L. and Kris S. warned that the recharge might not be
sufficient and to check float voltages with and w/o batteries
paralleled, to use batteries of comparable vintage, and to be sure extra
long run time didn't cause overheating.

I built an appropriate 12 Gauge cable and used the Run Time calibration
feature of the APC software. 4 batteries gave me no more run time than
pair A or pair B alone. I carefully rechecked connections, made sure no
connector was running hot and end up w. the same results. 4 batteries
give me the same run time as either pair. Total float current is about
12.5ma, 5ma on pair B, 7.5 on pair A).

I'm stumped. I've set things up so that I just pull off or stick back
on just one spade lug every time I do the test. What is going on?
I should be getting at least 2x the run time, (more since the slower
the consumption the more AH the battery yields.)

Any suggestions more than welcome.
Click to expand...

You may have already heard this, but:

If you've doubled the eneregy available to the APS and the run time has not
changed, then the APS is programmed to act on run time alone (and inform the
computer via the RS232/serial link) when it is time to quit. If you cannot
re-program the APS's messaging function, then you are out of luck, and the APS
manufacturer has won: You have to buy his bigger product.

webpa
 
WEBPA wrote:
Several weeks ago I posted a query here about the advisability and/or
precautions to take in paralleling batteries for a UPS, (an APC Smart
UPS-700 Net). It normally takes one pair of 12v 7AH batteries, from
which I was getting ~5-7 minutes of run time with a 65% load (as
reported by APC Powerchute Biz Edition 7.119).

Jerry G, Roni L. and Kris S. warned that the recharge might not be
sufficient and to check float voltages with and w/o batteries
paralleled, to use batteries of comparable vintage, and to be sure extra
long run time didn't cause overheating.

I built an appropriate 12 Gauge cable and used the Run Time calibration
feature of the APC software. 4 batteries gave me no more run time than
pair A or pair B alone. I carefully rechecked connections, made sure no
connector was running hot and end up w. the same results. 4 batteries
give me the same run time as either pair. Total float current is about
12.5ma, 5ma on pair B, 7.5 on pair A).

I'm stumped. I've set things up so that I just pull off or stick back
on just one spade lug every time I do the test. What is going on?
I should be getting at least 2x the run time, (more since the slower
the consumption the more AH the battery yields.)

Any suggestions more than welcome.




You may have already heard this, but:

If you've doubled the eneregy available to the APS and the run time has not
changed, then the APS is programmed to act on run time alone (and inform the
computer via the RS232/serial link) when it is time to quit. If you cannot
re-program the APS's messaging function, then you are out of luck, and the APS
manufacturer has won: You have to buy his bigger product.

webpa

You may be right. However, APC does provide a runtime calibration
Click to expand...
feature in their software which presumably should be able to appreciate
a larger battery. On the other hand, when the software is used with
their models specifically designed to take external battery packs, you
must tell the software how many extra packs have been attached; (perhaps
to recalibrate the AH curve?)
 
One possible solution is to parallel the batteries through series diodes,
preferably shcottky (to minimize voltage drops). If the batteries are
equally charged and the diodes nearly matched in terms of voltage drops you
will get load sharing. Even if you don't ,when one battery drops below the
other, the battery with the higher output voltage will start to provide
current to the load, and the weaker battery will be disconnected because its
associated diode will be reverse biased. Make sure the diodes can handle the
current. A heat sink may be required.


"WEBPA" <webpa@aol.com> wrote in message
news:20040403191515.03625.00000601@mb-m01.aol.com...
Several weeks ago I posted a query here about the advisability and/or
precautions to take in paralleling batteries for a UPS, (an APC Smart
UPS-700 Net). It normally takes one pair of 12v 7AH batteries, from
which I was getting ~5-7 minutes of run time with a 65% load (as
reported by APC Powerchute Biz Edition 7.119).

Jerry G, Roni L. and Kris S. warned that the recharge might not be
sufficient and to check float voltages with and w/o batteries
paralleled, to use batteries of comparable vintage, and to be sure extra
long run time didn't cause overheating.

I built an appropriate 12 Gauge cable and used the Run Time calibration
feature of the APC software. 4 batteries gave me no more run time than
pair A or pair B alone. I carefully rechecked connections, made sure no
connector was running hot and end up w. the same results. 4 batteries
give me the same run time as either pair. Total float current is about
12.5ma, 5ma on pair B, 7.5 on pair A).

I'm stumped. I've set things up so that I just pull off or stick back
on just one spade lug every time I do the test. What is going on?
I should be getting at least 2x the run time, (more since the slower
the consumption the more AH the battery yields.)

Any suggestions more than welcome.



You may have already heard this, but:

If you've doubled the eneregy available to the APS and the run time has
not
changed, then the APS is programmed to act on run time alone (and inform
the
computer via the RS232/serial link) when it is time to quit. If you
cannot
re-program the APS's messaging function, then you are out of luck, and the
APS
manufacturer has won: You have to buy his bigger product.

webpa
Click to expand...
 
be carefull you dont overload the internal
charger of the ups.

john

"WEBPA" <webpa@aol.com> wrote in message
news:20040403191515.03625.00000601@mb-m01.aol.com...
Several weeks ago I posted a query here about the advisability and/or
precautions to take in paralleling batteries for a UPS, (an APC Smart
UPS-700 Net). It normally takes one pair of 12v 7AH batteries, from
which I was getting ~5-7 minutes of run time with a 65% load (as
reported by APC Powerchute Biz Edition 7.119).

Jerry G, Roni L. and Kris S. warned that the recharge might not be
sufficient and to check float voltages with and w/o batteries
paralleled, to use batteries of comparable vintage, and to be sure extra
long run time didn't cause overheating.

I built an appropriate 12 Gauge cable and used the Run Time calibration
feature of the APC software. 4 batteries gave me no more run time than
pair A or pair B alone. I carefully rechecked connections, made sure no
connector was running hot and end up w. the same results. 4 batteries
give me the same run time as either pair. Total float current is about
12.5ma, 5ma on pair B, 7.5 on pair A).

I'm stumped. I've set things up so that I just pull off or stick back
on just one spade lug every time I do the test. What is going on?
I should be getting at least 2x the run time, (more since the slower
the consumption the more AH the battery yields.)

Any suggestions more than welcome.



You may have already heard this, but:

If you've doubled the eneregy available to the APS and the run time has
not
changed, then the APS is programmed to act on run time alone (and inform
the
computer via the RS232/serial link) when it is time to quit. If you
cannot
re-program the APS's messaging function, then you are out of luck, and the
APS
manufacturer has won: You have to buy his bigger product.

webpa
Click to expand...
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top